1. ELECTROMAGNETIC INTERACTIONS OF NEUTRINOS IN MATTER Int. School of Nuclear Physics Probing hadron structure with lepton & hadron beams

2. E.M. interactions of neutrinos 1)Radiative decays 2)Magnetic moment 3)Stimulated conversion … all GIM suppressed in vacuum! 2 1 W  l

3. Present limits Radiative decays SM theory:  0 = 7 10 43 (1eV/m) 5 (s) Pal & Wolfenstein (1982) Experiments: SN1987 (strong MH):  /m > 6 10 15 s/eV Bugey (mass degenerated):  m > 310 -4 s/eV if  m/m >10 -7 Solar eclipse :  m > 100 s/eV if  m 2 ~ 10 -5 eV 2 Magnetic moment SM theory:  = 3.2 10 -19 m(eV)  B Experiment (solar):  < 0.54 10 -10  B

4. Amplification in matter Coherent interactions on the atomic electrons e 2 W 1  e  0 /  m ~ 9 10 23 F(v)(N e /10 24 cm -3 ) 2 (1eV/m) 4 If mass-degenerated  0 /  m ~ 9 10 23 F(v)(N e /10 24 cm -3 ) 2 (1eV/m) 4 (m 2 /  m 2 ) 2 J.C.d’Olivo, J.F.Nieves (1989), G.Giunti et al. (1991)

5. Neutrino energy deposition in a Ge crystal Neutrino beam  High purity Ge diode 140 cm 3 at liquid nitrogen temperature (77K) Electron-hole pair creation work 3 eV: very low energy threshold Energy resolution ~ keV

6. Integral search: the principle A.Castera et al., Phys.Lett.B452, 150 High intensity beam: 20 GeV 10 13 pot in 4 ms spills, every 14 s 1 mip (muon) gives a sudden signal ~ 30 MeV in 5 cm Search: Continuous energy deposition building up during the spill duration

7. Results Clear on-beam signal of crossing mip’s No excess of deposited energy < 3 keV in 5 cm

8. Analysis 8 10 7  and anti-  per spill crossing the crystal Total energy deposition < 3 keV in 5 cm of Ge < 10 -5 eV /cm: 10 -12 normal dE/dx < 10 keV for whole earth diameter ~ 10 -2 eV /cm for weak interactions Case of mass-degenerated radiative decay E  = E  m 2 /m 2 = E 2  m/m 2 eV < E  < 200 eV 10 -10 <  m/m < 10 -8 Prob 5/3 10 -5  m 2 /m  0 > 1.5 10 18 m 3 /  m 2

9. An encore at the Bugey reactor Powerful source of anti- e : ~ 10 21 /s But also e from activation of the container: 55 Fe produces a peak at 230 keV and 51 Cr peak at 750 keV 15 m from the core: 4 10 9 /cm 2 for each of the 2 peaks  m /m > 3 10 -4 s/eV in Ge equivalent to   /m > 9 10 15 s/eV in vacuum

10. Stimulated conversion in an RF cavity Another way to amplify EM interactions M.C Gonzalès-Garcia, F. Vannucci and J. Castromonte Phys.Lett. B373,153(1996) Idea: an RF cavity is a photon bath (100W 10 9 QF~10 23  cm 3 à 10 -6 eV) Majorana neutrinos   anti- e ou anti-  Dirac neutrinos   sterile R =  N/N = (Q/10 9 )(P/100W)(m/eV) 3 (eV 2 /  m 2 ) 3 (s/  )  0 = 20/R (m/  m 2 ) 3  If R 2 10 18 s for  m 2 =10 -5 eV 2 and m=1 eV But also   +    +  

11. Recent development: sterile neutrinos What are sterile neutrinos? -Do not participate in Weak Interactions -Couple to the “real world” through mixing ( e, , , H …) = [U] ( 1, 2, 3, 4 …) Bad reasons: try to explain anomalies in past neutrino data LSND, MiniBoone, nuclear reactors, radioactive sources Good reasons: neutrinos are massive, need of Right Handed components Classical see-saw model, very high masses, but variations exist Every neutrino flux has some H component at the level of U Hl 2

12. Example: the MSM model Three sterile neutrinos, one of them having ~10 keV/c 2 mass Almost stable  DARK MATTER  Warm Dark Matter    7 10 43 (1eV/m) 5 (1/U 2 ) (s)

13. Cosmological limits Search of monoenergetic photons

14. Sterile neutrinos as WDM m( H ) ~ 7 keV U 2 ~ 10 -10 In vacuum:  0 = 4 10 34 s In matter:  m ~10 26 s Local Dark Matter density: 300 MeV/cm 3 Relative velocity: 200 km/s Flux of H on earth: 8 10 11 H /cm 2 s (yearly modulation) In crystal 1x1x1 m 3 : 10 -8 decay/year !! … 5 10 -4 /year in SK, 10/year in IceCube

15. Conclusion EM neutrino interactions exist in the Standard Model -Recent claim in astrophysics of radiative decay indication? They are hugely amplified in matter … but not yet enough to consider an experiment in the lab Unless nuclear physics help?